Each year, rice in Asia faces a big threat from a sesame-seed-sized insect called the brown plant hopper. Now, a study reveals the molecular switch that enables some plant hoppers to develop short wings and others long -- a major factor in their ability to invade new rice fields. The findings were published online on March 18, 2015 in Nature. Lodged in the stalks of rice plants, plant hoppers use their sucking mouthparts to siphon sap. Eventually the plants turn yellow and dry up, a condition called "hopper burn." Each year, plant hopper outbreaks destroy hundreds of thousands of acres of rice, the staple crop for roughly half the world's population. The insects have a developmental strategy that makes them particularly effective pests. When conditions in a rice field are good, young plant hoppers develop into adults with stubby wings that barely reach their middles. These short-winged adults cannot fly, but they are prolific breeders. A single short-winged female can lay more than 700 eggs in her lifetime. "The short-winged ones have great big fat abdomens. They're basically designed to stay put and reproduce," said biologist Dr. Fred Nijhout of Duke University, who co-authored the study with colleagues at Zhejiang University in China. But in the fall, as days get shorter and temperatures begin to drop -- signs that the rice plants they're munching on will soon disappear -- more plant hopper nymphs develop into slender adults with long wings. These long-winged plant hoppers lay fewer eggs, but are built for travel, eventually flying away to invade new rice fields. Until now, scientists did not know exactly how the shorter days and cooler temperatures triggered the shift between short and long wings, or which hormones were involved.
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